Purge system for electrostatic precipitator



P. HODSON May 10, I960 PURGE SYSTEM FOR ELECTROSTATIC PRECIPITATOR Filed Jan. 20, 1958 United States Patent i PURGE SYSTEM FOR ELECTROSTATIC PRECIPITATOR Peter Hudson, Wellsville, N.Y., assign'or to APRA Precipitator Corporation, New York, N.Y., a corporation of Delaware The present invention relates to gas cleaning apparatusor the like and, especially to an arrangement directing 'a high velocity fluid stream thru a predetermined portion of the apparatus to purge the dust particles from the collecting surfaces on which they have been deposited by a process of electrostatic precipitation.

'In gas cleaning apparatus of the electrostatic type dust laden gases are directed thru a strong electric field betweendischarge electrodes and grounded collector surfaces. As. the particles of dust entrained in the gases become electrically charged they move, under the. influence of the strong electric field, to the grounded collector surfaces on which they are deposited.

In order that the gas cleaning apparatus may be maintained at a high operating efficiency it is of primary importance that the electrodes and collecting surfaces be maintained relatively free from excessive deposits since the operating elficiency of such apparatus is, to a large extent, dependent upon the relative freedom of the collecting surfaces from deposited particles. Therefore, it becomes a primary object of this invention to provide an arrangement for efliciently removing the deposited particles from the collecting surfaces of an electrostatic precipitator to thereby prevent their becoming re-entrained in the clean gas stream issuing from the precipitator.

In steam boilers utilized in connection with present day installations for power generation the dust collecting surface must necessarily be so extensive that it is not feasible to purge all or even a large portion of the surface at one time since the demand for purging fluid would be far greater than may be made economically available, and furthermore the entire gas cleaning apparatus would necessarily be shut down to permit such a purging operation thereby momentarily destroying its power to remove particulate matter from the carrier gas.

Therefore, another object of this invention is to provide an arrangement which subjects only a small portion of the entire dust collecting surface to a purging action at any particular instant whereby a minimum flow of purging fluid is required to purge eflectively.

. A further object 'of this invention is to provide a purging arrangement having little interference with normal operation of the gas cleaning apparatus.

It is a still further object to provide a purging arrangement whereby the main gas flow is continued to all compartments except those being purged so that it is unnecessary to discontinue power during purging.

.The invention may be better understood by reference to the drawings in which:

Figure 1 is a partial assembly view of a precipitator purging arrangement according to this invention.

'Figure 2 is a sectional view of the precipitator purging arrangement.

Figure 3 is a schematic illustration of an operating mechanism for the switching rotor.

In the drawings the numeral designates the cylindrical housing of'an electrostatic precipitator having an inlet 12 atnhe bottom thru which a gaseous fluid enters to pass upward to outlet duct 14. The housing 10 is divided by annular partitions 16 and 18 into concentric compartments 22, 24 and 26 that are packed with banks of parallel tubes 20 or other collecting units adapted to separate the gaseous fluid from the particulate matter carried thereby.

An outlet duct 14 comprising a continuationof housing 10 is adapted to enclose a hood member 28 that is pivotally supported by a central rotor shaft 32. The rotor shaft 32 is rotated about its axis by a source of power not shown. The hood member 28 is preferably of sectorial configuration and is divided into a series of concentric passageways 34, 36 and 38 by arcuate partitions 42 and 44 that are in alignment with the annular partitions 16 and %18. Suitable sealing means 45 bridging the space between annular partitions 16 and 18 and the axial edges of arcuate partitions 42 and 44 are adapted to preclude the flow of fluid between adjacent passageways.

The passageways 34, 36 and 38 are directed radially inward where they join concentric chambers 46, 48 and 52 formed by the concentric ducts 47, 49 and 53 that extend axially into the purging fluid exhaust duct 54 carried by outlet duct 14.

The purging fluid exhaust duct 54 is divided into a plurality of superposed passageways 56, 57 and 58 by partitions 61 and 62 thereby providing a separate exhaust duct for each of the concentric chambers 46, 48 and 52. Aligned openings 64 in the outlet duct and its partitions 61 and 62 are adapted to receive the concentric ducts 47, 49 and 53, and a special rotary duct arrangement embodied therewith is adapted to provide means whereby gaseous fluids may be exhausted from the housing thru aligned passageways in the hood and the purging fluid exhaust duct.

The rotary duct arrangement between the concentric ducts 47, 49 and 53 and the superposed passageways 56, 57 and 58 has as its basis a perforate cylinder 66 which is in effect a continuation of outer duct 47. The cylinder is closed at its upper end by a plate 86 and is provided with annular series of openings '60 in alignment with each superposed duct 56, 57 or 58 to permit communication therebetween. Intermediate the annular series of openings imperforate portions of the cylinder 66 are adapted to lie in the same planes as the partitions 61 and 62 to provide surfaces with which sealing means 68 may cooperate to preclude the flow of fluid between passageways 56, 57 and 58.

(The central duct 53 terminates axially in the plane of partition 62, and an annular baflle 72 is adapted to extend between the end of said duct and the imperforate portion of the cylinder 66 lying axially between the an- -nular openings thereof. Similarly the concentric duct 49 terminates axially in the same plane as partition 61 and another annular baffle 74 is fitted between the end of said duct 49 and the imperforate portion of cylinder 66 which lies in alignment with the partition 61. The outer duct 47 also terminates axially in the plane of duct 54 and here the sealing means or packing 68 is adapted to bridge the space between the periphery of the opening in the exhaust duct 54 and the outer surface of duct 47.

By this arrangement each passageway of the hood will be interconnected continuously thru the perforations of cylinder 66 to one of the exhaust ducts, 56, 57 M58 whereby fluid from the several annular compartments 22, 24 and '26 may be exhausted thru passageways that are at all times maintained independent.

A purge fan 76 mounted in purging duct 78 is connected to a predetermined one of exhaust ducts 56, 57 or 58 by means of a switching rotor 82. Rotation of the switching rotor between the various exhaust ducts 56, 57 or 58 connects'a predetermined one of the ducts and its interconnected passageways to the suction of purging fan 76 whereby the velocity of the fluid entering the housing 12 is increased substantially to afltord the purging action required to remove the collected dust from the collecting surfaces of compartments 22, 24 or 26 and carry it to the exhaust ducts and switching rotor 82.

When switching rotor 82is aligned with one sectionof the outlet duct (for example section 56 illustrated), the adjoining sections 57 and 58 are open to duct-59 which leads back to the main gas duct 14 so as to permit fluid flowing thru the open ended ducts to return to the main fluid outlet. Only that duct which is aligned with the purging fan 76 thru the switching rotor 82 is at any time subjected to the purging action of the fluid set in motion by the fan 76 since arcuate sealing means 77 limits the suction of fan 76 to the ducts aligned with switching rotor 82.

The switching rotor 82 is actuated by the rotation of gear means 84 on shaft extension 32 fixed to plate 86 on the cylindrical portion of the rotating hood. The gear means is adapted to rotate once for every three turns of the rotor and as the gear means 84 rotates it turns a camming device 85 including three 120 deg. camming sections which are offset 120 deg. from one another so that one camming section is always effective at a given point around its periphery. The camming sections operates 3 limit switches LS-l, LS-2 and LS-3 in succession and each of the limit switches in turn controls valving means in the actuator for the switching rotor 82 so that for each rotation of the hood 28 and shaft 32 the gear means 84 and attached camming device 85 rotates onethird revolution and the switching rotor is advanced one step.

Figure 3 more particularly illustrates an actuator adapted to provide suitable actuation for the switching rotor 82. Here the limit switches LS-l, LS-2 and LS-3 regulate supply valves V and V and exhaust valves V and V leading to an actuating cylinder 88 that receives a flow of pressurized actuating fluid thru inlet 89 from a source not here illustrated. The fluid within cylinder 88 positions a piston 93 and rod mechanism 90 that is pivotally attached to an operating arm 92 fixed to switching rotor 82. Rotation of gear means 84 and camming means 85 will energize the limit switches and when LS-1 is energized the operating arm 92 will be at the extreme right position illustrated in Figure 2. The stop means 94 will be down out of the way of arm 92. On being energized limit switch 1 opens valves V and V and closes valves V and V This permits actuating fluid to enter the cylinder thru valve V and move the piston 93 to the left so the switching rotor 82 may line up with the outlet of duct 58. After one revolution of the hood 28 and one-third revolution of the camming means 85, LS-2 is energized. This causes the mechanical stop 94 to rise, valves V and V to open and valves V and'V to close. Pressure fluid entering cylinder 88 thru V forces piston 93 to the right until operating arm 92 strikes stop means 94. At this setting the switching rotor 82 is aligned with duct 57 during a complete revolution of hood 28. After one complete revolution limit switch 3 is energized by the camming means 85. This switch is adapted to lower the stop 94 so the actuator 88-93 may complete its movement to the right and align switching rotor 82 with duct 56.

This sequence will then repeat itself once for each three rotations of hood 28 as long as the hood continues to rotate about its axis. As the hood 28 rotates around the housing 10 and sequentially covers the ends of the collecting tubes 20, only those collecting tubes which lie in the compartment aligned with purging duct 78 through switching rotor 82 will be subjected to a purging action while all other collecting tubes under the hood will remain open to the main fluid-flow through duct 59 and will therefore remain in continuous operation;

While I have described my invention with respect to the device illustrated it is evident that the number of 4 concentric chambers in housing 10 may be varied so long as the number of concentric passageways in the hood and the exhaust duct are made to agree therewith. In addition means 84 together with the camming means 85 must be adapted to any such variation whereby the switching rotor will be sequentially moved from duct to duct to subject all the concentric compartments of the housing to the purging action of fan 76. Similarly the actuator for switching rotor 82 may be varied and other changes and modifications may be made by those skilled in; the art without departure from the essence of my invention. What I claim is: 1. A purging system for gas cleaning apparatus or the like having a cylindrical housing including a multiplicity of axially disposed collecting tubes extending between inlet and outlet ends thereof; annular partitions concentric with said housing adapted to divide the housing into a plurality of concentric chambers; a sectorial outlet hood member at the outlet end of the housing ax-' ially supported to rotate adjacent the end of said housing; means dividing the outlet hood into concentric passageways in alignment with the concentric housing chambers; purging duct means for the flow of fluid away from said hood; and means selectively connecting one of the concentric hood passageways and its aligned housing chamber to the purging duct whereby fluid from a predetermined housing chamber and its aligned hood passageway may be directed to the purging duct. 7

2. A purging system for gas cleaning apparatus or the like having a cylindrical housing including a multiplicity of axially disposed collecting tubes extending between inlet and outlet ends thereof; annular partitions concentric with said housing adapted to divide the housing into a plurality of concentric chambers; hood means pivotally supported for rotation about the outlet end of said housing; means dividing the hood into concentric passageways in alignment with the concentric housing chambers; purging duct means interconnected with the passageways of said hood; and means adapted to selec-;

tively interconnect said duct with the concentric passageways of said hood. 7

3. A purging system for gas cleaning apparatus or the like having a cylindrical housing including a mult'i-p plicity of axially disposed collecting tubes extending between inlet and outlet ends thereof; annular partitions concentric with said housing adapted to divide the housing into a plurality of concentric chambers; hood means -duct to certain of said concentric hood passageways whereby fluid may be sequentially exhausted from the collecting tubes connected thereto. p

4. A purging system for a gas cleaning apparatus or the like having a cylindrical housing including a multiplicity of axially disposed collecting tubes extending between inlet and outlet ends thereof; annular partitions concentric with said housing adapted to divide the housing into a plurality of concentric chambers; a sector shaped hood member axially supported for rotation in a plane adjacent the outlet end of said housing; means dividing the hood member into concentric passageways in alignment with the concentric housing chambers; purging duct means adapted'to direct fluid flow away from said hood; a clean gas outlet duct adapted to direct cleaned gas away from said housing; and means selectively connecting one of the concentric housing chambers and its aligned hood passageway to said purging" duct while connecting the remaining passageways of said hood to the clean gas outlet duct.

5. A purging system for gas cleaning apparatus orthe like having a cylindrical housing including a multiq plicity of axially disposed collecting tubes extending between inlet and outlet ends thereof; annular partitions concentric with said housing adapted to divide the housing into a plurality of concentric chambers; a sectorial hood member at the outlet end of said housing axially pivoted to rotate in a plane adjacent said outlet end; means dividing the sectorial hood into concentric passageways in alignment with the concentric housing chambers; purging duct means for the flow of fluid away from said hood; means selectively connecting one of said hood passageways to said purging duct; and means producing an induced draft in said purging duct whereby fluid may be drawn from a hood passageway and its aligned housing chamber to the purging duct,

6. A purging system for gas cleaning apparatus or the like including a cylindrical housing having a multi plicity of axially disposed collecting units extending between inlet and outlet ends thereof to direct a flow of fluid therethrough; annular partitions concentric with said housing adapted to divide the housing into a plurality of concentric chambers; a sector shaped hood member at the outlet end of said housing axially supported to rotate in a plane adjacent the outlet end of said housing; partitions dividing the hood into concentric passageways aligned with the concentric chambers of said housing; purging duct means adapted to direct the flow of fluid away from the hood; means responsive to rotation of said hood adapted to sequentially connect one of the hood passageways to the purging duct; and means imparting an increased velocity to the fluid flowing through the purging duct and its aligned housing compartments whereby particulate matter deposited on the walls of said housing compartments is re-entrained and exhausted thru said purging duct.

7. A purging system for gas cleaning apparatus or the like including a cylindrical housing having a multiplicity of axially disposed collecting units extending between inlet and outlet ends thereof to direct a flow of fluid therethrough; annular partitions concentric with said housing adapted to divide the housing into a plurality of concentric chambers; a sector shaped hood member pivoted axially for rotation in a plane adjacent the outlet end of said housing; partition means dividing the hood into a plurality of concentric passageways aligned with the concentric chambers of said housing; a purging duct adapted to direct the flow of fluid away from said hood; a clean gas outlet duct aligned with the housing and adapted to educe cleaned gas therefrom; means selectively connecting one of the concentric housing chambers and its aligned hood passageway to the purging duct while simultaneously connecting other of said hood passageways and their aligned housing chambers to the clean gas outlet duct; and means in said purging duct adapted to impart an increased velocity to the fluid flowing thereinto concentric ducts aligned with the concentric housing chambers; an exhaust duct including a plurality of separate passageways adapted to direct the flow of fluid away from the passageways of said hood; port means in the concentric ducts of said hood adapted to connect each passageway of said hood with a single passageway of said exhaust duct whereby fluid flowing thru the concentric chambers of said housing is directed through aligned passageways in the hood and exhaust duct.

9. A purging system for gas cleaning apparatus or the like including a cylindrical housing having a multiplicity of axially disposed collecting units extending between a main fluid inlet and outlet thereof to direct a flow of fluid therethrough; annular concentric partitions adapted to divide the housing into a plurality of concentric chambers; rotary hood means pivoted axially of said housing for rotation in a plane adjacent the outlet end thereof; partition means dividing the hood into concentric ducts in alignment with the chambers of said housing; an exhaust duct including a plurality of separate passageways connected to the ducts of said hood; a purge duct including a iiow inducing fan adapted to draw fluid from the exhaust duct; and switching means responsive to rotation of said hood adapted to align the purge duct with one of the passageways of said exhaust duct while simultaneously connecting the other passageways of the exhaust duct to the main fluid outlet.

References Cited in the file of this patent UNITED STATES PATENTS 705,944 Mitchell July 29, 1902 2,369,649 Abrams Feb. 20, 1945 2,582,133 Karlsson Jan. 8, 1952 2,701,622 Hodson Feb. 8, 1955 FOREIGN PATENTS 152,441 Australia July 17, 1953 

